1. Field of the Invention
The present invention relates to a technology for controlling a current supply to a motor of a vehicle mirror device.
2. Description of the Related Art
A vehicle mirror device is a device that turns a mirror unit, which includes a mirror, to a predetermined position by using a drive motor. When the mirror unit has turned to a predetermined position and has stopped rotating, sometimes an overcurrent flows in the drive motor because of overloads. When an overcurrent flows in the motor, a current supply to the motor is immediately cut OFF to prevent the motor from being damaged.
For example, Japanese Patent Application Laid-open No. 2002-127824 discloses a conventional technology for controlling a vehicle mirror device (an electrically-retractable door mirror). The conventional vehicle mirror device is configured to turn a door mirror of a vehicle any position between two predetermined positions, i.e., a stretched position and a retracted position. The vehicle mirror device includes a drive motor, a switch, a time constant circuit, a first circuit, and a second circuit. The drive motor is driven to turn the door mirror to any position between the stretched position and the retracted position. The switch includes a first output terminal and a second output terminal. The switch switches over a polarity of a direct-current power supply, and is operated to supply a direct-current voltage to the drive motor. The time constant circuit is arranged between the switch and the drive motor. The first circuit is arranged between the first output terminal of the switch and one terminal of the drive motor. The second circuit is arranged between the second output terminal of the switch and the other terminal of the drive motor. Each of the first circuit and the second circuit includes an electronic switch, an overcurrent detecting unit, and a breaking switch. The electronic switch is switched ON/OFF in response to an electric signal output from the time constant circuit. The overcurrent detecting unit has a characteristic such that its resistance value increases depending on a current value flowing therein, and is series-connected to the electronic switch. The breaking switch turns OFF the electronic switch when a voltage value generated by the overcurrent detecting unit exceeds a predetermined threshold.
In the conventional vehicle mirror device, however, an electric current flowing in the drive motor is cut OFF when the current exceeds a fixed threshold. Because of this configuration, when a high battery voltage is applied to the drive motor, the current supply to the drive motor is cut OFF at the fixed threshold, although the drive motor can be further rotated.